1. Field of the Invention
The present invention relates to a method of and an apparatus for pelletizing a radioactive waste, and more particularly, to a method of and an apparatus for pelletizing a radioactive waste in which it is possible to shorten the compressing time required when a waste powder is to be compressed or press-molded into a pellet, and to prevent environmental pollution from being caused by the waste powder which may be scattered during the pelletizing operation.
2. Description of the Prior Arts
A radioactive waste has been increasingly produced by an atomic power plant concurrently with an increase in the quantity of produced electricity, and therefore, the need for volume-reducing treatment of a radioactive waste has been increased in order to ensure a storage space in a facility. One method of reducing the volume of a radioactive waste has heretofore been proposed in which a concentrated waste liquid (the main component is a soda sulfate) obtained from the concentration of a waste liquid regenerated from ion exchange resins which are produced in large quantities by a boiling water reactor and granular ion exchange resin slurry are dried and milled so as to remove water occupying a large percent of the volume of a radioactive waste, and the thus-treated powder is formed and solidified into a pellet by using a tablet type pelletizer, or alternatively, after inflammable solid wastes have been burnt, the thus-produced ashes are formed and solidified into a pellet by using the tablet type pelletizer.
Such method of pelletizing a radioactive waste by the use of the tablet type pelletizer is disclosed in the specifications of Japanese patent unexamined publication No. 100799/1983, Japanese patent unexamined publication No. 100800/1983, and Japanese patent unexamined publication No. 108497/1983. However, these publications only disclose a mixing ratio or a compressive force connected with a radioactive waste powder.
According to one of conventional pelletizing methods using the above-mentioned pelletizer, a radioactive waste powder is supplied into a powder receiving cavity formed in a pelletizing section of the pelletizer, and the powder is pelletized within a through bore of a pelletizing die which extends from one end facing the powder receiving cavity to the other end facing the atmosphere, by inserting a first pelletizing rod from the side of the one end of the through bore, through the cavity, into the through bore under condition that a second pelletizing rod is inserted into the through bore by a predetermined length through the other end into the through bore. The waste powder is thus pelletized in a compressed manner within the through bore. However, such prior-art method involves disadvantage in that compressed air is not easily discharged through the through bore and compressing time correspondingly becomes longer. This is because the gap between the first pelletizing rod and the through bore and that between the second pelletizing rod and the through bore constitute minute gaps having substantially the same size or width and the air compressed during the pelletizing or press-molding operation is expelled through the minute gaps out of the through bore. In addition, the above-mentioned method involves a problem in that the compressed air passes through the respective gaps between the through bore and both rods and flows into not only the powder receiving cavity but also the atmosphere, so that part of the waste powder is mixed with the air flowing into the atmosphere, thus raising the problem of environmental pollution.